A new polarised hot filament chemical vapor deposition process for homogeneous diamond nucleation on Si(100)

International audienceA new hot filament chemical vapor deposition with direct current plasma assistance (DC HFCVD) chamber has been designed for an intense nucleation and subsequent growth of diamond films on Si(100).Growth process as well as the If(V) characteristics of the DC discharge are reported. Gas phase constituents activation was obtained by a stable glow discharge between two grid electrodes coupled with two sets of parallel hot filaments settled in-between and polarised at the corresponding plasma potential. The sample is negatively biased with a small 10-15 V extraction potential with respect to the cathode grid.Such design allows to create a high density of both ions and radicals that are extracted and focussed onto the surface of the sample.The current density onto the sample can be finely tuned independently of the primary plasma.A homogeneous plasma fully covering the sample surface is visualized. Consequently, a high-density nucleation (>1010 cm-2) occurs

Density control of electrodeposited Ni nanoparticles/nanowires inside porous anodic alumina templates by an exponential anodization voltage decrease

International audiencePorous alumina templates have been fabricated by applying an exponential voltage decrease at the end of the anodization process. The time constant η of the exponential voltage function has been used to control the average thickness and the thickness distribution of the barrier layer at the bottom of the pores of the alumina structure. Depending on the η value, the thickness distribution of the barrier layer can be made very uniform or highly scattered, which allows us to subsequently fine tune the electrodeposition yield of nickel nanoparticles/nanowires at low voltage. As an illustration, the pore filling percentage with Ni has been varied, in a totallyreproducible manner, between ∼3 and 100%. Combined with the ability to vary the porediameter and repetition step over ∼2 orders of magnitude (by varying the anodization voltageand electrolyte type), the control of the pore filling percentage with metal particles/nanowires could bring novel approaches for the organization of nano-objects

Charge Transfer and Tunable Ambipolar Effect Induced by Assembly of Cu (II) Binuclear Complexes on Carbon Nanotube Field Effect Transistor Devices

International audienceAssembly of paramagnetic Cu2 complexes with a Schiff base scaffold possessing extended electron delocalization together with a quasi-planar structure onto carbon nanotubes induces a diameter-selective charge transfer from the complex to the nanotubes leading to an interestingly large and tunable ambipolar effect. We used complementary techniques such as electron paramagnetic resonance, absorption spectroscopy, and photoluminescence to ensure the success of the assembly process and the integrity of the complex in the nanohybrid. We carried out density functional theory type calculations to rationalize the experimental results,evidencing the selective enhanced interaction of the metal complexes with one type of nanotube

Comparing TEM and resonant Raman spectroscopy for diameter distribution assessment of single wall carbon nanotubes

International audienceCharacterization of single wall carbon nanotube (SWCNT) population plays a key role to study the influence of growth parameters during their formation. Despite this crucial step, statistical data extracted from more than one characterization technique are rarely compared in publications claiming for SWCNT growth selectivity. Transmission Electron Microscopy and Raman spectroscopy are widely used to obtain an accurate measurement of the SWCNT diameters [1]. We used both techniques and observed a systematic shift between the diameter distributions assessed by Raman spectroscopy and TEM imaging in our typical SWCNT samples, CVD grown on SiO2/Si wafers (Figure 1)[2]. TEM image analyses were performed on samples transferred on TEM grids using the methodology we proposed in [3] whereas Raman spectra are recorded on the as grown samples and tube diameters were deduced from their radial breathing mode by following a procedure widely used in the literature [4]. Observed shift can be as high as 0.4 nm, which represents 20 to 30 % of the diameter values while measurement accuracy is estimated to be equal to 0.05 nm for both techniques. Furthermore, small tube diameters below 1.2 nm seem to be under-detected by TEM with respect to Raman whereas the opposite trend is observed for tube diameters larger than 1.5 nm. In this work, we explore the comparison between TEM imaging and Raman spectroscopy capabilities for determining the diameter distribution of a CVD grown sample, in an effort to validate, or invalidate, currently used methodologies

Comparing TEM and resonant Raman spectroscopy for diameter distribution assessment of single wall carbon nanotubes

International audienceCharacterization of single wall carbon nanotube (SWCNT) population plays a key role to study the influence of growth parameters during their formation. Despite this crucial step, statistical data extracted from more than one characterization technique are rarely compared in publications claiming for SWCNT growth selectivity. Transmission Electron Microscopy and Raman spectroscopy are widely used to obtain an accurate measurement of the SWCNT diameters [1]. We used both techniques and observed a systematic shift between the diameter distributions assessed by Raman spectroscopy and TEM imaging in our typical SWCNT samples, CVD grown on SiO2/Si wafers (Figure 1)[2]. TEM image analyses were performed on samples transferred on TEM grids using the methodology we proposed in [3] whereas Raman spectra are recorded on the as grown samples and tube diameters were deduced from their radial breathing mode by following a procedure widely used in the literature [4]. Observed shift can be as high as 0.4 nm, which represents 20 to 30 % of the diameter values while measurement accuracy is estimated to be equal to 0.05 nm for both techniques. Furthermore, small tube diameters below 1.2 nm seem to be under-detected by TEM with respect to Raman whereas the opposite trend is observed for tube diameters larger than 1.5 nm. In this work, we explore the comparison between TEM imaging and Raman spectroscopy capabilities for determining the diameter distribution of a CVD grown sample, in an effort to validate, or invalidate, currently used methodologies

Negative differential resistance in photoassisted field emission from Si nanowires

International audienceField emission (FE) from semiconducting nanowires (NWs) is studied for expanding electron gun performances and functionality in terms of stability, brightness, and pulsed emission. Here, we report on a pronounced and robust double negative differential resistance (NDR) in the FE IV characteristics measured during photoassisted field emission experiments on highly crystalline p-type silicon NWs. The main feature is a double NDR in the current saturation regime, which can be modulated by both temperature and light intensity. These results contrast with previous FE studies in which only a barely noticeable single NDR was reported. Several mechanisms for the physical explanation of the NDR are currently under consideration: photogenerated carrier instabilities in the depletion region, which give rise to a pulsed space-charge current in the nanowire or tunneling through a double quantum well formed by confinement at the NW apex. Because NDRs are signatures of pulsed currents, these results suggest new functionalities for which pulsed electron sources can potentially be achieved at high repetition rates

Laser pyrolysis of carbon-nitrogen gas-phase compounds: An attempted approach to carbon nitride formation

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Production of iron-oxide nanoparticles by laser-induced pyrolysis of gaseous precursors

International audienceLaser-assisted pyrolysis in a continuous flow reactor has been applied to synthesise iron-oxide nanoparticles. The scope of the present contribution was to investigate the possibility of increasing the reaction yield in order to obtain powder amounts suitable for practical applications. To this aim, a gas mixture containing Fe(CO)5 and N2O has been submitted to CO2 c.w. laser pyrolysis. As a reaction sensitiser gas, SF6 has been preferred to C2H4 to avoid ethylene fragmentation in N2O presence and the formation of iron carbides. Due to unexpected SF6 dissociation, the synthesis process led to the preferential formation of iron fluoride compounds. Powder samples, submitted to calcining treatment (400°C, 3 h), showed an almost complete transformation to α- and γ-iron oxides retaining the nanostructure feature of the powder